Temozolomide (hereinafter referred to as “TMZ”), an alkylating agent for treatment of carcinoma, has a broad-spectrum bioactivity of anti-tumor [L. H. Tsang, et al. Cancer Chemother Pharmacol. 27 (1991): 342-346], which in particular has bioactivity for treatment neuroglioma (brain carcinoma) and malignant melanoma (skin carcinoma). In some western countries, the TMZ capsule had been approved to be used for the treatment of malignant neuroglioma. WO 0057867 described a method by using TMZ at a cyclical schedule. Also, the TMZ capsule has been approved to be used clinically in China. Phase II clinical trials showed that TMZ had activity for curing malignant melanoma [N. M. Bleehen, et al. J. Clin. Oncol. 13 (1995): 910-913], and recent phase III clinical trials revealed that TMZ has the same activity as the dacarbazine for curing malignant melanoma [M. R. Middleton, et al. J. Clin. Oncol. 18 (2000): 158-166] even with the similar side effects between them such as leucocytopenia, nausea, vomit, hair loss, red rash and constipation. Besides, oral administration of TMZ displayed dose-limiting myelotoxicity [A. M. Heimberger, et al. Clin. Can. Res. 6 (2000): 4148-4153]. Previous study on changing formulation exhibited that intrathecal injection administration of TMZ solution could decrease the side effects [J. H. Sampson, et al. Clin. Can. Res. 5 (1999): 1183-1188]. So it should be deemed that the transdermal formulation is the ideal for TMZ to cure skin carcinoma, especially during the early period. Some studies have proven that local administration of toremifene on site of carcinoma might result in a high local concentration, while lowering the systematic concentration [L. Soe, et al. Cancer Chemother. Pharmacol., 39 (1997): 513-520], which brought about lower systematic toxicity.
Generally, percutaneous administration is conditioned by both the skin barrier and the physicochemical properties of drug. Instability and insolubility of said drug prevent it from being made into formulations. Studies, as published in WO0057867, showed that its inability to permeate artificial skin (silicon membrane), rat skin and human skin rendered it impossible to be made into transdermal formulations. In view of this, the application of TMZ will be limited to a great extent.
Previously, aiming at structure modification, a lot of derivatives has been synthesized, most of which were focused on replacement of substitute group at nitrogen atom of No. 3 and the modification of substitute group at nitrogen atom of amide group of No. 8. The general formula, as described in EP0252682 (1987), claimed methyl, ethyl, propyl and butyl temozolomide-8-carboxylates, but didn't disclose their pharmacological actions and the activities for treatment of carcinomas.
On the other hand, the compounds of imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, typically represented by TMZ, share a common trait of so bad solubility, that they can hardly be dissolved in any common-used solvents such as ethyl acetate, dichloromethane and water. They exhibit a slight solubility of about 1˜5% in the blend of organic solvent and water, for example the aqueous solution of acetic acid, acetonitrile, acetone, methanol or ethanol with the concentration of 1˜10%. Even in the non-protonic polar solvent-DMSO, their solubility is about 5%. In addition, another trait of these compounds is their instability, which is embodied not simply by their sensibility to light, what is more, by their sensibility to alkaline mediums with pH value more than 7 and those mediums with nucleophilic group such as the compounds containing amidogen, hydroxyl and mercapto group. For example, the environment of the pH value more than 7 will make these compounds rapidly decomposing and changing color (red); the same story may occur in the methanol and ethanol. It is therefore limited for the methanol and ethanol to be used as the solubilizer in manufacturing preparations. So it seems to be much desired to develop a novel bioactive compound and to seek the methods for enhancing its stability and solubility in the application of the pharmaceutical industry.